auth/credentials: if credentials have principal set, they are not anonymous anymore

auth/credentials: if credentials have principal set, they are not anonymous anymore

When dealing with Kerberos, we cannot consider credentials anonymous
if credentials were obtained properly.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11265

Signed-off-by: Alexander Bokovoy <ab@samba.org>
Reviewed-by: Stefan (metze) Metzmacher <metze@samba.org>
Reviewed-by: Guenther Deschner <gd@samba.org>
Autobuild-User(master): Alexander Bokovoy <ab@samba.org>
Autobuild-Date(master): Wed Jul 15 16:32:55 CEST 2015 on sn-devel-104

(cherry picked from commit a0d2dd0e01618346b4ad8ea9da3f7ce4eb0364b0)

Autobuild-User(v4-2-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-2-test): Thu Jul 16 14:11:52 CEST 2015 on sn-devel-104